Recently, the operating voltage of various types of electronic appliances has gradually decreased. As an example, Microcontroller Units (MCUs) and main chip products, which operate at a voltage of 0.9 to 1.0V, have recently been developed.
As the operating voltage of electronic devices decreases in this way, the output voltage of a voltage regulator for driving the electronic devices must also gradually decrease. That is, as the power supply voltage that must be supplied to drive the MCUs and the main chips gradually decreases, a voltage regulator is increasingly required to output a stable and low output voltage.
FIG. 1 is a block diagram of a conventional low output voltage regulator, and FIG. 2 is a graph showing the ultra low dropout characteristics of a conventional low output voltage regulator.
As shown in FIG. 1, a conventional low output voltage regulator 1 includes a chip enable unit 10, a reference voltage generation unit (1.2V voltage reference) 20, an error amplification stage (error AMP) 30, an overload protection unit 40, a gate drive stage 50, a pass element 60, and a voltage division circuit (resistive feedback network) 70.
The chip enable unit 10 outputs an enable signal so as to directly supply power to respective functional blocks.
The reference voltage generation unit 20 receives an initial voltage signal, and divides the initial voltage signal into connected circuit units, thus setting voltage and current to a reference voltage within an output range. The reference voltage generation unit 20 generates the reference voltage to be compared to a divided voltage, the divided voltage being generated through the division of input voltage by the voltage division circuit 70, which is composed of a transistor and a trimming feedback resistor.
The error amplification stage 30 compares the reference voltage, output from the reference voltage generation unit 20, with the divided voltage, output from the voltage division circuit 70, and thus amplifies the difference between the voltages.
The overload protection unit 40 includes a thermal shutdown stage 41, which is provided with a plurality of transistors, diodes, and resistors, is adapted to compare the signal generated by the reference voltage generation unit 20 with output voltage, and is operated to decrease the output voltage when an overload occurs or when the temperature increases beyond a certain temperature while operation is not in a normal mode, a switching control stage 43, which stabilizes the signal output from the thermal shutdown stage 41 and transmits the output signal to an output interface, and an overcurrent protection stage 42.
The pass element 60, which passes only a stable voltage through a selected interface, is stabilized by the gate drive stage 50 and is adjusted to a certain level.
However, the conventional low output voltage regulator is problematic in that, since it is constructed to allow the chip enable unit 10 to supply power to respective functional blocks, power is shut off by only the logic-off operation of the chip in a disabled state, in which the driving of the chip is stopped, and thus standby power is continuously consumed.
Further, the conventional low output voltage regulator is problematic in that, when the reference voltage generation unit 20 outputs a low reference voltage, an internal feedback voltage is very low, so that a separate process for a low voltage MOS transistor (Metal Oxide Semiconductor Field Effect Transistor: MOSFET) must be added, or a deep sub-micron process below 0.18□ is required, in order to allow the transistor of the input stage of a differential amplifier to have a low threshold voltage (Vt).
Further, the conventional low output voltage regulator is problematic in that, since the voltage division circuit 70 has a resistor structure composed of trimming pads, the size of the regulator chip is increased, and thus the manufacturing costs thereof are increased.
Moreover, when the voltage regulator chip, which is a power Integrated Circuit (IC), is broken, or when the temperature thereof reaches a temperature at which the normal operation of the voltage regulator is difficult, the thermal shutdown stage 41 of the overload protection unit 40 of the conventional low output voltage regulator must accurately and stably stop the driving of the chip at high speed. Further, when the temperature decreases again, the thermal shutdown stage 41 must resume normal operation.
Meanwhile, as shown in FIG. 2, the conventional low output voltage regulator starts to exhibit ultra low dropout characteristics only when the input voltage becomes equal to or greater than a minimum input voltage VIN,MIN enabling the normal operation of the circuit, regardless of the ULDO. In other words, when an output voltage Voutput is greater than the difference between the minimum input voltage VIN,MIN and the ultra low dropout VDROPOUT, normal ULDO can be obtained.
However, recently, when low output voltage is required to supply power supply voltage for MCUs and main chips, the voltages of which have gradually decreased, that is, when low input voltage less than the minimum input voltage VIN,MIN is desired to be converted into a low output voltage V01 or VO2, there is a problem in that voltage dropout greater than the ultra low dropout VDROPOUT occurs.